The use of precast concrete facing elements to cover the exposed face of a composite gravity retaining structure is known. Such known composite structure comprises layers of particulate backfill material which alternate with layers of reinforcing members attached to facing elements. The primary binding force is the frictional interaction between the particulate material and the strips of reinforcing elements. U.S. Pat. Nos. 3,421,326 and 4,557,634 typify this known earth stabilization technique. U.S. Pat. No. '634 includes facing elements having frontally projecting buttresses and inwardly inclined facing surfaces to provide an exposed horizontal planting bed for each row of panels and is specifically distinguished over an earth stabilization structure having an essentially continuous concrete face as vertical walls and as in the present invention.
U.S. Pat. No. 4,449,857 discloses a vertically disposed retaining structure having a welded wire grid system providing small frictional forces along the wires of the grid perpendicular to the face and mechanical anchorage along the wires parallel to the face. In this prior art system, a required cast-in-place concrete footing forms a levelling pad without any potential for accommodating a variety of landscaping vegetation to mask the front of the panel. The total weight of each individual facing element is necessarily additive. Thus, the resultant foundational load will tend to overload the bearing capacity of the soil at the front toe of the structure defined at the lower front edge of the vertical retaining wall. Construction of the U.S. Pat. No. '857 vertical retaining wall requires external bracing structures so that the stacked facing elements will remain standing until tie-back wire anchors are applied and backfilled soil is disposed behind the vertical wall.
Further vertically disposed retaining wall structures are disclosed in U.S. Pat. Nos. 4,068,482; 4,343,572; 4,616,959; and 4,662,794. U.S. Pat. No. '482 discloses the use of anchoring elements or vertical tie rods used in combination with other laterally disposed anchoring means. U.S. Pat. No. '572 is a poured-in-place structure with the end of a wire grid system cast-in-place for subsequent attachment of a flexible wire grid. Each of the U.S. Pat. Nos. '959 and '794 discloses vertically disposed facing elements in combination with mats or sheets of preformed perforate mats extending therebehind. Such vertically disposed walls preclude vegetative growth and produce significant foundation loads requiring a poured-in-place base structure.
U.S. Pat. Nos. 2,210,218; 4,050,254; and 4,572,711 disclose facing elements disposed at an angled slope incline and dependent upon a frictional force between a horizontally extending leg and the backfilled soil behind the facing elements to function as a retaining structure. While these modular structures rely upon gravity, the related system operates at limited heights because of the weak resistance to forward sliding within the backfilled soil. Tie-back elements are precast and must extend rearwardly for a significant distance to develop the frictional force required to avoid sliding of the wall in a forward direction under the influence of the pressure caused by the backfilled soil mass. U.S. Pat. No. '218 is very unstable in heights greater than one foot because no provision is made to resist the horizontal earth pressure behind the back of the wall.
U.S. Pat. Nos. 2,880,588 and 3,254,490 disclose sloped retaining wall structures requiring large cast-in-place concrete footings. Furthermore, upright columns are used in combination with the horizontal facing elements. Thus, these systems are not gravity earth retaining systems.
U.S. Pat. Nos. 4,426,176; 4,512,685; 4,671,706; 4,711,606; and 4,459,858 are gravity retaining wall structures wherein stacked individual facing elements produce a relatively large mass to retain an earth mass behind them. The stability of these known structures is related directly to the mass of the structure compared to the height of the backfill. Thus, usefulness of these prior art designs is limited by the large mass required at taller wall heights, i.e., the structural mass required to safely retain the earth becomes so great, economical wall construction is not possible because of the multiplicity or size of the modular units at the bottom thereof. U.S. Pat. Nos. '176, '685 and '606 show various types of anchorage systems to establish large footings or simply gain mass for supporting the large additive vertical loads of individual facing elements piled one on top of the other. The webbed anchor of U.S. Pat. No. '706 does little to stabilize the backfilled earth or prevent overturning of the wall facing if a failure were to occur. U.S. Pat. No. '858 discloses a precast concrete chain forming a dead-man anchor assembly providing no assurance of preventing wall movement in the horizontal direction due to earth pressure behind the wall.